The invention relates to a pneumatic shock absorber comprised of at least the following components:
An upper support plate;
a lower part, which may be designed in the form of a piston, laminated spring or the like, and which comprises a lower mounting plate;
a bellows acted upon by pressure and made of elastomeric material and connecting the upper support plate and the lower component with each other, using fastening means (e.g. clamping rings); as well as
a height sensor.
For raising the riding comfort and the safety in modern rail-borne vehicles, systems are increasingly employed for controlling the level of height, for adapting the height of the vehicles, for diagnosing defects and for continuously monitoring the condition of the vehicle. As secondary suspension means, pneumatic shock absorbers are very often used. Their height can be varied by feeding or blowing off compressed air as required according to the given load and/or driving conditions. For this purpose, the pneumatic springs are coupled with systems for determining with the help of such systems either the height of the pneumatic shock absorber directly or the spacing between two parts moving in relation to each other (for example the superstructure of the railroad car and a suitable fixed pivot point on the bogie). In the simplest case, use is made for said purpose of mechanical lever systems that are pivot-mounted, for example on one side of the bogie in a fixed site, and connected on the other side with a lever mechanism that is located on a control valve mounted on the superstructure of the railroad car. When a relative movement occurs between the bogie and the superstructure of the railroad car, a reaction of the control valve is triggered by the setting of said lever in such a manner that compressed air is either supplied or blown off. Such systems have the drawback that they have a response accuracy that can be adjusted in a fixed manner only once. A high response accuracy does in fact permit adequately good and rapid regulation of the level in the standstill condition (for example when the height of the rail vehicle is adjusted for the first time), but leads to undesirable continuous reactions of the control valve when the vehicle is moving. With a lower response accuracy, on the other hand, it is possible to continually supply or blow-off compressed air (for example when short rail shocks occur as it may be the case when driving through rail switches); however, controlling the height at a standstill, in particular when the height of the rail vehicle is adjusted for the first time, is clearly made more difficult.
For this reason, systems are increasingly gaining importance in which height sensors are employed for determining the variations in the level in the presence of relative movements between the bogie and the superstructure of the railroad vehicle. The values measured by such height sensors are processed in a control unit, which then generates corresponding control signals transmitted to the control valves, whereby short-time changes in the measured values can be filtered out. Known are, for example height sensors that are installed in the interior of the pneumatic shock absorber. Changes in the height are detected by such height sensors inductively (DE 34 46 411 A1; DE 40 35 784 A1; DE 44 13 559 A1), or by means of ultrasound (DE 36 20 957 A1; DE 34 23 602 A1; U.S. Pat. No. 4,798,369). Pressure sensors that are mounted on the outer wall of a roll-off piston and actuated by the pneumatic shock absorber bellows rolling off on the roll-off piston, are known as well (DE 42 43 530 A2). However, the applicability of each of said solutions is limited to pneumatic suspension systems whose pneumatic suspension bellows are designed in the form of a so-called tubular rolling bellows, and which are capable of substantially performing only vertical movements in the direction of their longitudinal axis. Such pneumatic suspension systems are primarily employed in motor vehicles.
Substantial deflections in the horizontal direction occur to some extent in connection with rail-borne vehicles, thus perpendicular to the operating direction of the pneumatic shock absorber. Such deflections can be absorbed only by pneumatic shock absorber bellows designed in the form of so-called semi-rolling bellows. A solution for installing a height sensor in such a pneumatic suspension system is described, for example in published patent DE 296 20 721 U1. In said known system, a mechanical height sensor comprised of a lower component (which, as a rule, is a laminated spring) and an upper component (=the upper support plate) is installed in such a manner that a tappet actuated by spring force is pressed against the upper component, whereas the housing of the sensor is installed in the lower component in a fixed manner. The change in the distance of travel of the tappet is converted into an electrical signal and supplied to a control unit. Such a solution is disclosed in Japanese patent specification 4-266 632 as well. However, owing to the mechanical and electronic components of a height sensor designed in such a way, as well as to the stroke of the tappet that has to be realized, the result is necessarily a minimum length of the height sensor conditioned by the construction, which, in particular in conjunction with flat pneumatic suspension systems, leads to the fact that components of the height sensor protrude from the pneumatic suspension system. This may lead to substantial installation problems especially if the pneumatic suspension system is mounted with its lower component on a support of the bogie. Furthermore, installation cases are known in which the pneumatic suspension system is directly connected with an additional pressure reservoir via the lower component. In such a case, the installed height sensor obstructs the exchange of air between the pneumatic suspension system and the additional pressure reservoir. This could be compensated only with a complicated type of construction of the lower component, in which suitable channels would have to be provided for the exchange of air.
Feasible solutions for such complicated installation conditions are introduced, for example in patent specifications DE 196 48 112 C1 and DE 197 01 713 C1. Patent document DE 196 48 112 C1 introduces an ultrasound sensor installed on the side of the vehicle undercarriage. The reflector component of said ultrasound sensor has a lens-shaped, convex surface, with the area normal of said surface being directed at the transmitting/receiving component. Apart from the fact that the reflector component has to be manufactured with a great amount of expenditure, such a solution is not employable in connection with large horizontal deflections of the pneumatic shock absorber as they occur in connection with rail-borne vehicles. The same applies to the solution introduced in patent specification DE 197 01 713 C1 as well, where an ultrasound sensor is installed in the compressed air feed line. In both cases, the horizontal deflection of the pneumatic shock absorber leads to the fact that no continuously stable signal path is assured between the transmitting and receiving units and the ultrasound sensor.
Therefore, the invention is based on the problem of avoiding the described drawbacks of the known technical solutions, and of introducing a solution that can be produced at favorable cost and permits the change in height of a pneumatic shock absorber to be determined in a simple manner, taking into account the horizontal deflections, in cases where the installation of a height sensor in the interior of the pneumatic shock absorber is not possible because of lack of space above and/or below the pneumatic shock absorber for the components of the height sensor projecting from the pneumatic shock absorber, or in cases where the pneumatic shock absorber is directly connected with an additional pressure reservoir and the exchange of air would be interrupted or obstructed by a height sensor installed in the interior of the pneumatic shock absorber.
For solving said problem, the pneumatic shock absorber as defined by the invention is characterized according to the characterizing part of claim 1 in that an upper extension arm extends sideways from the upper support plate, and a lower extension arm extends sideways from the lower mounting plate, whereby the height sensor is positioned between the two extension arms.
Useful variations of the pneumatic shock absorber as defined by the invention are specified in claims 2 to 7.